The present invention provides a new method of catalytic epoxidation of ethylenically unsaturated compounds.
The oldest industrial technique epoxidizing double bonds is the procedure via the chlorohydrin which uses chlorine as the oxidizing agent. This method has its disadvantges, in particular the simultaneous production of calcium chloride as a by-product of the dehydrochlorination of the chlorohydrin which has low economic value.
It is also known that ethylene can be epoxidized in good yield in the vapor phase by molecular oxygen over a catalyst based on silver. However such technique is not applicable to olefins in general because it lacks selectivity and give rise to undesired by-products of oxidation.
Other epoxidation methods have been proposed which carry out oxidation by air in two steps. For example, in U.S. Pat. No. 3,351,635 a hydrocarbon such as isobutane or ethylbenzene is oxidized by air to a corresponding hydroperoxide. This intermediate hydroperoxide is then reacted with the olefin in the presence of a compound of vanadium, molybdenum or tungsten. However this method has the disadvantage of producing a low-cost alcohol as a by-product in amount chemically equivalent to the epoxidized compound formed.
It has also been proposed to exploit hydrogen peroxide as an oxidizing agent in the presence of a catalyst such as tungstic acid or in the presence of a nitrile as disclosed in U.S. Pat. No. 3,053,856. These two methods also are not satisfactory, because in the first case the epoxide is not obtained but the corresponding glycol is obtained instead, whereas in the second case there is obtained along with the epoxide an equivalent quantity of the amide corresponding to the starting nitrile. The economic interest for such a method is thus strongly dependent on the value of the by-product.
There has also been described in Belgium Pat. No. 747,316 a method whereby hydrogen peroxide is utilized as epoxidation agent in the presence of a catalyst based on organic derivatives of tin. However, the latter compounds have not been available industrially.